Anti-tarnish process using dicyandiamide formaldehyde condensation product

ABSTRACT

THE CLEAN SURFACE OF METALS, SUCH AS COPPER AND COPPER-CONTAINING ALLOY ARTICLES, CAN BE PROTECTED FROM TARNISHING BY CONTACTING SUCH SURFACE WITH A CONDENSATION PRODUCT OF DYCYANDIAMIDE AND FORMALDEHYDE. THE PREFERRED COMPOSITION FOR USE IN THIS PROCESS CONTAINS THE CONDENSATION PRODUCT AND A NONIONIC OR ANIONIC SURFACTANT. THIS COMPOSITION IS GENERALLY MIXED WITH WATER AND THE CLEAN SURFACE IS DIPPED IN OR OTHERWISE CONTACTED WITH THE AQUEOUS SOLUTION.

United States Patent O 3,639,646 ANTI-TARNISH PROCESS USING DICYANDI- AMIDE FORMALDEHYDE CONDENSATION PRODUCT Peter Jochen Borchert, Elkhart, Ind., James Edward Slager, Edwardsburg, Mich., and Ronald George Sommer, Mishawaka, and Mitchell Frank Zienty, Ellrhart, IndI, assignors to Miles Laboratories, Inc., Elkhart, Ind. No Drawing. Filed Mar. 28, 1969, Ser. No. 811,602 Int. Cl. C02b 5/06; C08g 9/14 U.S. Cl. 252-18ll 6 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND AND PRIOR ART Metal objects, such as fittings, tubing and the like formed from copper and copper-containing alloys, generally are severely tarnished in their finished form, and it is commercially desirable tarnished in their finished form, and it is commercially desirable to remove such tarnish before they are supplied to the ultimate users of such items. The prior art cleaning techniques for removing tarnish generally consisted of first treating the tarnished article with a detergent cleaning bath to remove greases, oils, soap, borax and waxes which resulted from the operations employed to form the article. The cleaned item was then exposed to a descaling bath, which in the case of copper articles generally contained sodium cyanide. Sulfuric acid has also been used in prior art descaling baths. After passing through the descaling bath, the item was then treated with a bright dip bath which in the case of copper articles generally contained nitric acid or a mixture of chromic acid and sodium bisulfate. The finished item had a clean bright surface.

When the bright dip bath contains chromic acid, the resulting bright copper surface, for example, is passivated and will not readily tarnish through subsequent handling or atmospheric reaction. However, if nitric acid is used in the bright dip bath, the resulting copper surfaces, for example, is activated and will readily tarnish through subsequent handling or atmospheric reaction. A similar situation exists when the prior art descaling and bright dip baths are replaced by a single cleaning composition containing citric acid, a metal chloride, a ferric salt and a nonionic surfactant. This latter composition produces a clean bright metal surface which is somewhat activated.

The prior art has suggested the use of benzotriazole to treat such activated surfaces, such as copper surfaces, in order to prevent tarnishing, but ,this treatment has not been entirely satisfactory since it is difficult to get uniform protection with this material. Even with a reasonably good coating, the article can still tarnish in an undesirably short time.

DESCRIPTION OF THE INVENTION In accordance with the present invention anti-tarnish protection for metal surfaces is provided by a process comprising contacting such surface with a condensation product of dicyandiamide and formaldehyde. The preferred composition for use in this process is a mixture of the condensation product and a nonionic or anionic surfactant. The components of this composition preferably are in the proportion of l-lOO weight parts of a condensation product of dicyandiamide and formaldehyde and 0.01-5 weight parts of the nonionic or anionic surfactant. This composition can be dissolved in water to form an aqueous solution containing 0.l-l0 weight per cent of a condensation product of dicyandiamide and formaldehyde and 0.001-05 weight percent of a nonionic or anionic surfactant.

The condensation products of dicyandiamide and formaldehyde useful in the process and composition of the present invention are well known in the art. Generally such condensation products are prepared by mixing dicyandiamide, formaldehyde and a catalyst, such as ammonium chloride, and allowing the exothermic reaction to heat the mixture to about -100 C. The dicyandiamide-formaldehyde condensation product preferably employed in the present invention is prepared by forming an aqueous slurry of 1.5-2.0 moles of formaldehyde and 1 mole of dicyandiamide, adding stepwise to the slurry 0.3 to 0.6 mole of a catalyst, such as ammonium chloride, in amounts to maintain the temperature of the reaction mixture below about C. and to maintain the pH of the reaction mixture initially between about 1.0 and about 2.5 and upon completion of the reaction be tween about 2.5 and about 3.5, carrying out the reaction at a temperature below about 70 C. and at a pH below about 3.5 until a water-soluble reaction product having an average molecular Weight of about 500 to about 700 is obtained, and then cooling the reaction product to room temperature. Upon standing at room temperature, the pH of the reaction mixture will gradually increase within about 2 hours to about 3.8-4.2.

The nonionic or anionic surfactants useful in the present composition are well known materials. Typical nonionic surfactants are N-(beta-hydroxyethyl)laurylamide, nonylphenylpolyethylene glycol ether, octylphenylpoly ethylene glycol ether, sorbitan monooleate, polyoxyethylene sorbitan tristearate, ethoxylated isomeric linear alcohols and the like. The ethoxylated isomeric linear alcohols have the formula:

wherein n is a number from 9 to 13 and y is a number from 3 to 12. The preferred nonionic surfactant is a nonylphenylpolyethylene glycol ether having the formula:

wherein at is an integer having a value of from 5 to 70. Preferably x has a value of from 5 to 40.

Typical anionic surfactants useful in the present composition are C C straight-chain saturated carboxylic acids; alkali metal salts of C -C straight-chain saturated carboxylic acids, such as sodium stearate; dodecylbenzene sulfonic acid; sodium lauryl sulfoacetate; monoethanolamine lauryl ether sulfate and the like.

The anti-tarnish composition of the present invention:is most conveniently employed in the form of an aqueous solution. The initial pH of such solution should be in the range of from 3.5 to 8.0 and preferably in the range from 4.5 to 6.0. If necessary, appropriate acidic or basic materials can be added to adjust the pH to the above values.

In carrying out the process of the present invention, the metal surface can be contacted with the anti-tarnish composition at temperatures from about 25 C. to about 95 0., preferably at a temperature of about 95 C. The article to be treated is contacted 'with a solution of the composition, for example, for from 30 seconds to 3 minutes, preferably for about 1.5 to 3 minutes, and then dried. This contact can take place by immersing the article in the solution, or the solution can be sprayed, for example, onto the metal surface. The metal surface can also be contacted with a viscous gel or paste containing the antitarnish composition.

The invention is described in further detail in the following examples.

EXAMPLE 1 A mixture of 5 weight parts of a condensation product of dicyandiamide and formaldehyde prepared by the above-described preferred procedure and 0.4 weight parts of a nonionic surfactant having the formula:

wherein x was 9-10, was blended and mixed with sufficient water to form an aqueous solution containing 0.5 weight percent of the condensation product and 0.04 weight percent nonionic surfactant. This solution had a pH in the range from 4.5 to 6.0.

A tarnished copper article was cleaned with a mixture of citric acid, sodium chloride, ferric sulfate and nonionic surfactant until the surface was bright. This cleaned bright article was then immersed in the above anti-tarnish solution at 85-95 C. for 1.5 minutes. The article was then removed from the solution, dnained for 1.5 minutes and then air dried. The resulting treated article, having a uniform pinkish-copper color without water marks, was stable to tarnishing by atmosphere moisture, carbon dioxide, air and casual amounts of atmospheric conta-minants. The thus treated article was also subjected to periodic handling wherein contact was made between the article and human fingers. After several months of such exposure and handling, the treated article was free of finger marks and was substantially stable to tarnishing from other sources.

EXAMPLE 2 A mixture of 182 grams of a 55 weight percent aqueous solution of the condensation product of dicyandiamide and formaldehyde prepared by the above-described preferred procedure and 2 grams of a nonionic surfactant having the formula:

wherein at was 30-40, was mixed with 815 grams of water to form an aqueous solution containing 10 weight percent of the condensation product and 0.2 weight percent of the nonionic surfactant. A 130 grams portion of finelydivided silica thickening agent was then added to such solution to form a paste.

A tarnished copper pipe was cleaned as described in [Example 1. The above paste was applied to part of the clean pipe surface and allowed to remain for 1 minute. It was then removed with a damp cloth. The pipe was then placed in a 90 C. oven for 16 hours. At the end 4 of that time the portion of the pipe treated by the above paste was still clean and bright, while the remainder of the pipe surface was badly tarnished.

While the above disclosure is directed principally at anti-tarnish treatment of copper and copper-containing alloys, such as brass and bronze, it should be understood that the anti-tarnish composition and process of the present invention is useful for protection of any metal surface subject to tarnishing.

What is claimed is:

1. A process for protecting a metal surface from tarnishing which comprises contacting such surface with a condensation product of dicyandiamide and formaldehyde.

2. A process according to claim 1 wherein the condensation product of dicyandiamide and formaldehyde is in an aqueous mixture which also includes a nonionic or anionic surfactant.

3. A process according to claim 2 wherein the aqueous mixture contains components in the proportions of 1 to weight parts of a condensation product of dicyandiamide and formaldehyde and 0.01 to 5 weight parts of a nonionic or anionic surfactant.

4. A process according to claim 2 wherein the surfactant is a nonionic nonylphenylpolyethylene glycol ether.

5. A process according to claim 4. wherein the surfactant has the formula:

where x is an integer having a value of from 5 to 70.

6. A process according to claim 2 wherein the aqueous solution contains 0.1 to 10 weight percent of a condensation product of dicyandiamide and formaldehyde and 0.001 to 0.5 weight percent of a nonionic or anionic surfactant.

References Cited UNITED STATES PATENTS 2,384,467 9/1945 Hill 26069 X 2,425,320 8/1947 Hill 26069 X 2,526,106 10/1950 Albrecht 874 2,934,523 4/1960 Albrecht 26069 X 2,950,268 8/1960 Cofrancesco 260-69 3,015,649 1/1962 Zorn 26069 3,223,513 12/1965 Geary 26069 X 3,248,235 4/1966 Pryor 106-3 JOHN T. GOO LKASIAN, Primary Examiner M. E. McCAMISH, Assistant Examiner US. Cl. X.R.

2l2.5; 106--3; l342; 25282; 26029.4, 69 N 

